The Endless Winter (2011)

From the introduction

The Endless Winter is a Dungeons and Dragons adventure designed for four to six 12th level characters.

The winter in and around the city of Mysara has been particularly harsh this year. Normally they got moderately low temperatures and a little snow, but this year has been brutal: frigid cold temperatures, several feet of snow and miserable conditions. It has caused the death of dozens and the destruction of crops that the residents depend on for survival.

Lord Tyras Silverleaf, governor of the city of Mysara, commanded his son Derran to gather his best troops and set out to find the source of the climate change. Two weeks passed and they group has not been heard from since